Cathode ray tube deflection system utilizing an auxiliary electron beam



y 13, 1965 D. CHARLES 3,195,008 CATHODE RAY TUBE DEFLECTION SYSTEM UTILIZING AN AUXILIARY ELECTRON BEAM Filed April 9, 1963 SIGNAL SOURCE INVENTOR 2 Daniel CHA RLES @Qwm- Mav- ATTORNEY United States Patent 3,195,fid CATHUEE RAY TUBE DEFLEQTIQN SYSTEM UTE- LEZHNG AN ATJXELEARY ELECTRQN BEAM Daniel Charles, Paris, France, assignor to CSF-Compa nie Generale de Telegraphic Sans Fil, Paris, France Filed Apr. 9, E63, Ser. No. 271,639 Claims priority, application France, Apr. 12, T962,

94, 1%) Claims. (ill. 3l51%) The present invention relates to cathode ray tubes and more particularly to the deflection systems for these tubes which provide the electron beam deflection along orthogonal directions to produce a scanning of the beam in accordance with a time base provided by signals of periodically variable voltage.

When the periodically variable deflection voltages have a very high frequency, the electrostatic deflection by condenser plates is no longer utilizable by reason of the finite time taken by the electrons to traverse the deflection space. For that reason, one utilizes, according to a well-known technique, cathode ray tubes in which the pair of deflection plates is replaced by a delay line with wave propagation which causes the high frequency wave to travel with a phase velocity equal to that of the electrons in such a way that the transit time of the electrons practically no longer intervenes.

However, such an arrangement necessitates very high accelerating voltages and from this fact the sensitivity of the system is reduced. The low sensitivity is due, additionally, to the inherent weakness of the coupling between the electron beam and the wave propagating along the line.

The present invention has as its object a new deflection system, insensitive to the transit time of the electrons of the cathode beam, and presenting an increased efliciency with respect to that obtained with the known systems.

The present invention is based on the principle that an electron beam, penetrating into a space without electric field, expands therein by the effect of the space charges, while the extent of the expansion along a given path is a function of the perveance of the beam.

Taking advantage of this phenomenon, the present in vention provides for the placing of a thin beam, which one desires to deflect as a function of signals of variable amplitude, in the immediate victinity of a large beam of which one is able to cause the perveance to vary by means of the said signals. One may note under these conditions that the thin beam undergoes deviations or deflections which follow the expansion of the wide beam.

Consequently, the cathode ray tube according to the present invention is characterized by the fact that it comprises means for producing first and second electron beams, propagating parallelly one to the other within an electric field in front of a common anode and expanding by the effect of. the space charges within a space without electric field to the rear of the said anode, the cross section of the first beam being very small in comparison with that of the second beam, a luminescent screen receiving exclusively the electrons of the first beam, a collec tor receiving exclusively the electrons of the second beam, and means to cause the perveance or" the second beam to vary in accordance with a high frequency signal voltage in such a manner as to cause the angle of expansion of the electrons within the fieldless space to vary thereby also causing the first beam to deviate or deflect from its initial path.

Accordingly, it is an object of the present invention to provide a cathode ray tube, and more particularly a deflection system which obviates by simple means the drawbacks and shortcomings encountered with the prior art systems.

?atented July 13, 1965 ice It is another object of the present invention to provide a novel deflection system for cathode ray tubes which may be utilized with relatively high frequency deflection signals without the drawbacks imposed normally by the transit time of the electrons.

A further object of the present invention resides in the provision of a deflection system for cathode ray tubes which permits use of high frequency deflection signals without loss in sensitivity of the instrument.

A still further object of the present invention resides in the provision of a deflection system for cathode ray tubes, offering an efliciency that is substantially increased with respect to that obtainable heretofore with the known prior art systems and requiring relatively lower voltages than the known deflection systems which seek to adapt cathode ray tube deflection systems for use with high frequency deflection signals.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows in the single figure thereof, for purposes of illustration only, a cathode ray tube provided with a deflection system in accordance with the present invention.

Referring now to the drawing which shows, in longitudinal cross section, a cathode ray tube in accordance with the present invention of which the enclosure is evacuated in the usual manner, the tube illustrated therein comprises a metallic wall 1, a glass wall 2, traversed by the current supply conductors 3, and another glass wall 4 in the upper portion of the enclosure. The wall 4 carries at its internal surface an aluminized luminescent screen 5 in front of which is disposed a post-accelerating grid 6.

The-lower portion of the enclosure terminates in a collector 7 of truncated conical shape, provided with cooling fins 8.

In the upper portion of the enclosure is disposed an electron gun of the usual type as is conventional with cathode ray tubes. This gun comprises a cathode 9, a Wehnelt electrode 10, a first anode 11, a second anode 12 and a final anode 13, provided with a passage aperture 14.

In the lower portion of the enclosure one can readily recognize a triode constituted by a cathode 15, a control grid 16 and the extension of the plate 13 which forms part of the electron gun and comprises, opposite the grid 16, a passage aperture 17, covered by a grid 18 with a large transparency. The anode 13 is therefore common to the triode and tothe electron gun.

A voltage source 19 provides the various electrodes of the electron gun and of the triode with appropriate bias voltages with respect to the cathode 9 and 15, connected with each other, the positive terminal of the voltage source 19 being connected to the metallic wall 1 of the enclosure to which are also connected the anode 13 and the post-accelerating grid 6.

A voltage source 20 establishes an elevated diflerence of potential between the screen 5 and the post-accelerating grid 6, the negative terminal of this source being connected to the metallic wall 1.

The cathodes are heated either directly or indirectly by usual means, not illustrated in the drawing.

Reference numeral 21 indicates a pair of deflection plates intended to receive a linear voltage to cause the electrons passing between the plates to be deviated perpendicularly to the plane of the figure of the drawing.

Finally, a variable voltage signal source 22 is connected to the control grid 16 across a coupling condenser 23, the circuit of the grid comprising a discharge or leakage resistance 26.

In operation, the electron gun produces a thin electron beam 24, and the triode furnishes a beam 25 that is much larger. The two beams traverse the common anode 13 and enter the space behind this anode which is aspace without electric field. Now, it is known that under these conditions a parallel electron beam expands due to the effect of the. space charges and that the extensiveness of expansion, for a given distance, is a function of the perveance P of the beam, given by the expression:

inwhich I is the current of the beam and V the accelerating voltage of an equivalent diode which would produce the beam 25.

The variable voltages of the source 22, applied to the control grid 16, cause the intensity of the beam 25 to vary and therewith its perveance, and the beam 25 expands depending on the value of these voltages.

Now, the two neighboring beams, separated by a relatively very insignificant interval, may be considered as one in which the perveance is determined by the intensity of the larger beam 25, alongside of which the intensity of the small beam 24 is practically negligible. Effectively, one notesunder these conditions that the trajectory of the beam 24 is little different from that followed by the electrons which move along the adjacent rim of the beam 25.

The electrons of the beam 25 are collected by the collector 7 whereas the beam 24, deviated at 26 within the space Without field and strongly accelerated after passage through the post-accelerating grid 6, impinges on the luminescent screen at impact points of which the distance from the initial position varies as a function of the variable voltages applied to the grid 16.

The beam 25 isthus utilized tocausethe beam 24 to vary along one axis of the ordinates whereas the deviations along an axis of the abscissae take place in the usual mannerby means of the, pair of condenser plates 21 between which one applies a sweep voltage, for example, of saw-tooth waveshape, supplied by a time base, not illustrated on the drawing.

The deviations of the beam 24, obtained by causing the perveance of the beam 25. to vary by the variable voltages of the source 22, are independent of the transit time of the electrons and the arrangement described may be utilized, consequently, irrespective of the frequency of these voltages. The tube described may therefore serve in all applications in which a need exists for a deflection system for very high frequencies.

While I have shown and described one embodiment in accordance with the present invention, it is obvious that the same is not limited to the details shown and described herein but is susceptible of numerous changes and modifications as known to a person skilled in the art, and I therefore do not wish to be limited to these details but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

Iclaim:

1. A cathode ray tube comprising:

a target and collector means axially spaced from said target in said cathode ray tube,

a portion of the tube forming a space devoid of any electric field, an electron gun for. producing a first electron beam propagating through said space toward said target,

means for producing a second electron beam and having a substantially greater, cross sectional area than said first beam propagating side-by-side with said first-mentioned beam toward said collector means,

and means for modulating the perveance of said second beam in accordance with high frequency signals to thereby vary the angle of expansion of said second beam for deflecting said first beam.

2. A cathode ray tube comprising:

luminescent screen means,

means within said tube constituting a space devoid of any electric field,

5 electron gun means for producing a first electron beam propagating within said space toward said screen means,

a pair of parallel deflection plates for electrostatically deflecting said first beam in a first plane, substan- 10 tially perpendicular to said plates,

means for producing a second electron beam propagating side-by-side with said first beam and having a substantially greater cross sectional area than said first beam, the axes of said two beams being disposed in a second plane substantially parallel to said plates,

and means for modulating the intensity of said second beam in accordance with high frequency signals thereby varying the angle of expansion of said second beam and therewith deflecting said first beam in said second plane.

3. A deflection system for deflecting an electron beam and operable substantially independently of the transit time of the electrons, comprising:

means for producing a first electron beam passing through a space substantially devoid of any electric field,

and means for deflecting said first beam by signals including means for producing a second electron beam propagating side-by-side with said first beam and means for varying the perveance of said second beam by said signals to thereby vary the angle of expansion of said second beam and therewith deflecting said first beam.

4. A deflection system for deflecting an electron beam at relatively high frequencies, comprising:

means for producing said electron beam,

and means for deflecting said first-mentioned electron beam including means for producing a second electron beam propagating side-by-side with said firstmentioned beam and operable to deflect said firstmentioned beam by changes in the perveance of the second beam.

5. A cathode ray tube comprising:

luminescent screen means,

means within said tube constituting a space devoid of any electric field,

electron gun means for producing a first electron beam propagating within said space toward said screen means,

means for producing a second electron beam propagating side-by-side in close proximity to said first beam,

and means for modulating the perveance of said second beam in accordance with high frequency signals thereby varying the angle of expansion of said seccond beam and therewith deflecting said first beam in a predetermined plane.

6. A deflection system for deflecting an electron beam within a cathode ray tube provided with an evacuated enclosure and operable substantially independently of the transit time of the electrons, comprising:

screen means, means for producing a first electron beam propagating toward said screen means and passing through a space substantially devoid of any electric field, and means for deflecting said first beam by .signals including means for producing a second electron beam propagating side-by-side with said first beam and means within the enclosure of said tube constituting a a substantially greater cross sectional area than said first beam propagating side-by-side with said first beam. 7

7. A deflection system for deflecting an electron beam at realtively high frequencies, comprising:

means for producing said electron beam which propagates through a space substantially devoid of any electric field,

and means for deflecting said first-mentioned electron beam including means for producing a second electron beam and having a substantially greater cross sectional area than said first mentioned electron beam propagating side-by-side in close proximity to said first-mentioned beam and operable to deflect said first-mentioned beam by changes in the perveance 0f the second beam.

8. A cathode ray tube provided with an enclosure adapted to be evacuated and comprising:

luminescent screen means,

means within the enclosure of said tube constituting a space devoid of any electric field,

electron gun means for producing a first electron beam propagating within said space toward said screen means,

a pair of parallel deflection plates for electrostatically deflecting said first beam in a first plane, substantially perpendicular to said plates,

means for producing a second electron beam and having a substantally greater cross sectional area than said first beam propagating side-by-side with said first beam, the axes of said two beams being disposed in a second plane substantially parallel to said plates,

and means for modulating the perveance of said second beam in accordance with high frequency signals thereby varying the angle of expansion of said second beam and therewith deflecting said first beam in said second plane.

9. In a cathode ray tube provided with an evacuated enclosure and having luminescent screen means, electron gun means for producing a first electron beam propagatthe improvement essentially consisting of a deflection system for deflecting said first beam in a second plane including means for producing a second electron beam propagating side-by-side with said first beam, and means for modulating the intensity of said second beam in accordance with signals thereby varying the angle of expansion of said second beam and therewith deflecting said first beam in said second plane. 10. In a cathode ray tube provided with an evacuated enclosure and having luminescent screen means, electron gun means for producing a first electron beam propagating toward said screen means, and first deflection means for deflecting said first beam in a first plane,

the improvement essentially consisting of a deflection system for deflecting said first beam in a second plane including means for producing 'a second electron beam propagating side-by-side with said first beam and having a substantially greater cross sectional area than said first beam, both of said beams passing through a space portion in said tube substantially devoid of any electric field, and means for modulating the intensity of said second beam in accordance with signals thereby varying the angle of expansion of said second beam and therewith defiecting said first beam in said second plane.

The International Dictionary of Physics and Electronics, Van Nostrand Co., Inc., p. 663.

ing toward said screen means, and first deflection means 35 DAVID G. REDINBAUGH, Primary Examiner.

for deflecting said first beam in a first plane, 

1. A CATHODE RAY TUBE COMPRISING: A TARGET AND COLLECTOR MEANS AXIALLY SPACED FROM SAID TARGET IN SAID CATHODE RAY TUBE, A PORTION OF THE TUBE FORMING A SPACE DEVOID OF ANY ELECTRIC FIELD, AN ELECTRON GUN FOR PRODUCING A FIRST ELECTRON BEAM PROPAGATING THROUGH SAID SPACE TOWARD SAID TARGET, MEANS FOR PRODUCING A SECOND ELECTRON BEAM AND HAVING A SUBSTANTIALLY GREATER CROSS SECTIONAL AREA THAN SAID FIRST BEAM PROPAGATING SIDE-BY-SIDE WITH SAID FIRST-MENTIONED BEAM TOWARD SAID COLLECTOR MEANS, AND MEANS FOR MODULATING THE PERVEANCE OF SAID SECOND BEAM IN ACCORDANCE WITH HIGH FREQUENCY SIGNALS TO THEREBY VARY THE ANGLE OF EXPANSION OF SAID SECOND BEAM FOR DEFLECTING SAID FIRST BEAM. 